You can modify the amount of each ingredient according to taste. This is a Thermomix récipe, but you can also make it easily using traditional methods.
Ingredients (8-10 servings)
380g whole milk
100g whisky (or more, according to how strong you like it!)
1 small tin condensed milk (370g)
20g pure dark chocolate (I use ‘Valor’ or ‘Bourneville’)
Place the chocolate in the jug and grind at máximum speed for a few seconds.
Add the remaining ingredients and mix for 5 minutes, 50ºC at Speed 2.
Pour into a bottle and chill until needed. Shake every day or two. Serve with ice.